Field of the Invention
The present invention relates to an image processing apparatus that processes an image obtained by performing imaging of a subject's eye, a control method therefor, and a storage medium storing a program that causes a computer to execute the control method.
Description of the Related Art
In diagnostic imaging in ophthalmology as an example, recent use of a tomographic image in addition to an eye fundus image that has been widely used allows three-dimensional observation of an internal state of a retinal layer of an eye of a subject (subject's eye). Thus, a diagnosis made by using a tomographic image is expected to be useful for making a more accurate diagnosis of a disease.
The above-described eye fundus image is captured by using a fundus camera, scanning laser ophthalmoscope (SLO), or infrared (IR) rays, for example. The above-described tomographic image is captured by using an optical coherence tomography (OCT) instrument, for example.
In recent years, there have been provided apparatuses that enable follow-up observation of the internal state of the retinal layer of a subject's eye by using the above OCT instrument, thus enabling observation of the development of a disease or the postoperative clinical course. In follow-up observation of a subject's eye, a newly acquired tomographic image is compared with a tomographic image of the same site acquired in the past. This comparison between the images is typically made by displaying the newly acquired tomographic image and the tomographic image acquired in the past simultaneously (hereinafter referred to as “follow-up display”). This follow-up display facilitates a comparative understanding of corresponding portions from two tomographic images and is very useful for follow-up observation.
With improvements in technology, it has become possible for an OCT apparatus that captures a tomographic image to capture a tomographic image of a wider region in a single imaging session. There are also facilities having a plurality of OCT apparatuses with different imaging performance (for example, the size of an image capturing region whose image can be captured). For example, in Japanese Patent Laid-Open No. 2014-14727, a technique is proposed in which, in the case where a region whose image can be captured is enlarged as a result of the improved performance of a tomographic image capturing apparatus, imaging conditions for a tomographic image to be captured for follow-up observation are set.
In the case where follow-up observation of a subject's eye is carried out, a follow-up display is most often used as described above. For example, in the case of a facility having a plurality of OCT apparatuses with different sizes (dimensions) of image capturing regions, there is a situation in which a captured tomographic image whose image capturing region is different in size from that of a tomographic image captured in the past has to be used in follow-up observation of an eye of a subject. In this case, when an attempt to display all image regions of each tomographic image within a predetermined follow-up display range is made, one tomographic image is reduced or enlarged in size to be displayed because the sizes of the respective image capturing regions are different. In this case, since two tomographic images have a different display scaling factor, for example, the thicknesses of cross sections of the subject's eye may not be accurately compared with each other, raising a concern that this may make effective follow-up observation difficult.
Thus, it is considered that the entirety of each tomographic image is displayed at an original scaling factor on a follow-up display screen. In this case, however, the tomographic image whose image capturing region is large (wide) contains an image region not used for comparison, thereby making a comparative understanding of corresponding portions between the tomographic images difficult and increasing the burden of follow-up observation on an examiner. In this regard, the technique disclosed in Japanese Patent Laid-Open No. 2014-14727 is a technique of simply setting imaging conditions for the case where a tomographic image whose image capturing region is enlarged with respect to a past tomographic image is captured, and thus it is difficult to solve this issue.